The present application relates to an apparatus for, and a method of, recording sub data to the reflective layer of an optical-disk recording medium to which main data is recorded as a combination of pits and lands by forming corresponding marks on the reflective layer. The present invention is also directed to a method of producing such an optical-disk recording medium.
Among optical disks, the ROM (read-only memory) disk is widely used as a package medium because many replica substrates thereof can be produced inexpensively in a short time by injection molding of plastics with a single stamper. For example, CD (Compact Disk), DVD (Digital Versatile Disk), etc. are widely prevalent as ROM disks to record information such as music, video, etc.
Disks having illegally copied thereto data recorded in a ROM disk sold as a package medium, the so-called pirate disks, have been produced and have violated the copyright for the data in the ROM disk in the past.
Generally, pirate disks are produced by forming a stamper by mastering on the basis of signals read from a normal-version disk and replicating optical disks by the stamper, or by copying signals read from the normal-version disk to many recordable disks.
Various techniques have been proposed heretofore to prevent the production of such pirate disks. A well-known one of such techniques is to append unique identification information to each of disks, for example. There can be built a system in which unique identification information is appended with this technique to each disk and a disk player reads the identification information and sends it to an external server via a network. If many such pirates disks have been produced and distributed, a large amount of the same identification information will be sent to the external server and thus such a system can detect that the pirate disks have been distributed. Further, the system can also identify a pirate-disk producer or distributor by identifying a disk player having sent the identification information to the external server.
However, even the identification information unique to each disk should be recorded in such a manner as to prevent easy copying by a commercially available disk drive, so as to be useful for protection of the copyright for the main data in the disk.
In this regard, it was proposed to record the identification information by forming corresponding marks on the reflective layer of a disk (see, Japanese Patent No. 3454410). More specifically, in the disk disclosed in Japanese Patent No. 3454410, main data (content data, management information or the like) is recorded as a combination of pits and lands, while sub data (identification information) is recorded in addition to the main data to the disk by forming, on the reflective layer of the disk, marks which will give a small change in reflectance to a portion of the reflective layer which is above a predetermined one of the pits or lands.
The marks are recorded to the reflective layer by irradiating laser light higher in power than the reading laser light. The change in reflectance caused by the mark is so small that reading of the main data recorded as a combination of pits and lands will not be influenced, namely, that the sub data will not be read during normal reading of the main data.
To read the sub data itself, a separate playback system may be provided to sample many parts of the read signal of the main data, each given the small change in reflectance, and integrate the samples, for example.
In this case, a position where a mark is to be inserted as sub data is determined according to a predetermined algorithm. That is, with the normal-version disk player, it is possible to identify a position where the mark is to be recorded according to the similar algorithm to an algorithm used for recording and thus read the identification information as the sub data accurately.
Referring now to FIG. 1, there is schematically illustrated the internal structure of a sub data recorder designed based on the technique disclosed in Japanese Patent No. 3454410. The sub data recorder is generally indicated with a reference numeral 50.
As above, the sub data is identification information unique to each disk. Therefore, the sub data recorder 50 is to record sub data in a unique pattern to each of disks loaded therein.
Also, the sub data is recorded in a predetermined section on the disk, and each mark is inserted in a predetermined position in the section. The sub data recorder 50 is designed to record a mark in such a predetermined position.
First, a disk D is placed on a turntable (not shown), and a spindle motor 51 rotates the disk D by a predetermined rotation driving method. An optical pickup OP shown in FIG. 1 reads recording signal (main data) from the disc D being thus rotated.
The optical pickup OP includes a laser diode LD to emit laser light, objective lens 52 to condense and focus the laser light emitted from the laser diode LD onto the recording surface of the disk D, photodetector PD to detect a return part, from the disk D, of the laser light irradiated to the disk D, etc. as shown in FIG. 1.
The return part of the irradiated laser light or return light detected by the photodetector PD in the optical pickup OP is converted by an IV conversion circuit 53 into an electrical signal, and then supplied to a matrix circuit 54. The matrix circuit 54 generates a read signal RF, tracking error signal TE and focus error signal FE on the basis of the return light information supplied from the IV conversion circuit 53.
The sub data recorder 50 also includes a servo circuit 55 that controls a tracking drive signal TD and focus drive signal FD supplied from a biaxial drive circuit 56 on the basis of the tracking error signal TE and focus error signal FE supplied from the matrix circuit 54. The controlled tracking drive signal TD and focus drive signal FD are supplied to a biaxial mechanism (not shown) that holds the objective lens 52 inside the optical pickup OP and makes tracking servo control and focus servo control of the objective lens 52.
Also, the read signal RF generated by the matrix circuit 54 is equalized by an equalizer (EQ) 57 and then supplied to a binarization circuit 59 in which it will be converted into a binary data “0” or “1”, The binary data is supplied to a PLL (Phase-Locked Loop) circuit 60, sync detection circuit 61 and address detection circuit 62.
Also, the read signal RF from the matrix circuit 54 is supplied to a center level detection circuit 58 that will detect a center level of the read signal RF. The center level is used for binarization in the binarization circuit 59.
The PLL circuit 60 generates a master clock CLK synchronous with the supplied binary data, and supplies it as an operation clock to each of appropriate system components, especially, to the equalizer 57 and binarization circuit 59 as well as to a synchronization detection circuit 61, address detection circuit 62 and sub data generator 63, which will be explained below.
The PLL circuit 60 generates a PLL error signal from a phase difference between an edge pulse resulted from slicing made of the read signal RF in the binarization circuit 59 on the basis of the center level and an output signal (master clock CLK) from an internal VCO (Voltage-Controlled Oscillator), and feeds it back to the VCO to generate the master clock CLK synchronous with the binary data as above.
The sync detection circuit 61 generates a frame sync signal on the basis of the result of detection of a sync pattern in the supplied binary data, and supplies it to each of the appropriate system components, such as the address detection circuit 62.
The address detection circuit 62 detects address information ADR on the basis of the frame sync signal and supplied binary data. The address information ADR is supplied to a controller (not shown) that controls the entire sub data recorder 50. In the controller, the address information ADR is used for seeking etc. The address information ADR is also supplied to a writing timing generation circuit 64 in the sub data generator 63.
The sub data generator 63 includes the writing timing generation circuit 64 and a RAM (Random-Access Memory) 65 as shown. The sub data generator 63 generates, based on an input sub data, address information ADR and master clock CLK, a writing timing signal Wrt intended for recording marks to be recorded as sub data in predetermined positions on the disk D.
Here will be briefly described the operations made in the sub data generator 63 for recording the sub data.
First, it is assumed here that marks as sub data are to be recorded on a predetermined-length one of pits and lands recorded in combination as main data on the disk D (see FIG. 7, for example).
To this end, the sub data generator 63 has to generate the writing timing signal Wrt that will take a high level (H level) at a time when the predetermined-length one of the pits or lands as the main data is reached. To generate such a writing timing signal Wrt, the RAM 65 in the sub data generator 63 has stored therein the content of main data to be recorded to the disk D.
The sub data is identification information unique to each disk D as also mentioned above. Such a unique identification information is supplied to the writing timing generation circuit 64 in the sub data generator 63 each time a disk D is loaded into the sub data recorder 50.
The writing timing generation circuit 64 identifies the position of a predetermined-length one of pits or lands as the main data stored in the RAM 65, and generates the writing timing signal Wrt at a time corresponding to the pit or land position. Since a mark is to be recorded actually in a bit position at the center (third bit position in case of 5 T, for example), so the writing timing signal Wrt is generated which will take the H level at a time corresponding to the central bit position.
A laser power controller 66 is also included in the sub data recorder 50 to control the laser output of the laser diode LD in the optical pickup OP on the basis of a writing timing signal Wrt supplied from the sub data generator 63. More specifically, the laser power controller 66 controls the laser diode LD to emit laser light having a reading power when the writing timing signal Wrt is at a low level (L level). Also, the laser power controller 66 controls the laser diode LD to emit laser light having a writing power when the writing timing signal Wrt is at the H level.
With irradiation of the writing-power laser light emitted from the laser diode LF under the control of the laser power controller 66, marks will be formed as sub data in laser-irradiated portions of the reflective layer of the disk D.
FIG. 2 shows waveforms indicative of recording operations made in the sub data recorder 50 constructed as shown in FIG. 1.
First, the center level is detected by the center level detection circuit 58 on the basis of the read signal RF. Based on the detected center level, there is generated an edge pulse indicating edge timing of pits and lands formed on the disk D.
As also mentioned above, the PLL circuit 60 generates a PLL error signal corresponding to a phase difference between the above edge pulse and the output pulse from the VCO, and the PLL signal is fed back to the VCO to generate a correct master clock CLK synchronous with the binary signal.
When recording marks as sub data on the disk D in the sub data recorder 50 shown in FIG. 1, the laser power controller 66 controls the laser diode LD to provide laser light having the writing power.
Thus, since the photodiode PD in the optical pickup OP will detect strong return light from the disk D in a section in which the writing timing signal Wrt takes the H level, so the read signal RF in this section will correspondingly have a waveform in which a writing pulse is superposed on the read signal RF as shown and have the value thereof increased to a very high level.
If the read signal RF has the level thereof thus abruptly elevated in the mark-recorded portion, it will not have a value which is normally obtainable and thus the edge pulse will also be erroneous.
FIG. 2 shows an example in which the mark as sub data is recorded on each predetermined-length pit or land. However, especially in case the mark is to be formed on the pit portion, there exists a high possibility that the edge pulse will be erroneous. That is, though the read signal RF on the pit portion should normally have a negative value, a writing pulse will be superposed on the read signal RF due to the mark recording as above so that the value of the read signal RF will increase to a level higher than the center level as shown being encircled (indicated with a reference symbol X) in FIG. 2. With the read signal value higher than the center level, there will be generated an edge pulse which should normally be impossible.
If the edge pulse is thus generated in incorrect timing, the PLL error signal also becomes erroneous as shown and the timing of the master clock CLK controlled based on the erroneous PLL error signal is also erroneous. The error the master clock CLK incurs will cause the system components of the sub data recorder 50 to operate incorrectly.
Among others, the writing timing signal Wrt is generated by the writing timing generation circuit 64 in timing of the master clock CLK during recording to instruct the laser power controller 66 for correct timing of recording. Thus, because of the erroneous master clock CLK, the marks as sub data cannot be recorded in correct positions.
Also, if the master clock CLK is erroneous, the address detection circuit 62 cannot detect address information ADR accurately.
Also, if the read signal RF has the value thereof abruptly increased in a portion of the disk D where the mark is to be recorded as mentioned above, the center level detected based on the read signal RF will disadvantageously be higher than a normal level (see the level indicated with a reference symbol Y in FIG. 2).
If an elevation of the center level also makes it impossible to correctly generate an edge pulse, the master clock CLK will be erroneous.
That is, the above elevation of the center level makes it impossible to record the mark in a correct inserting position as above and detect address information accurately.
Further, in the sub data recorder 50 constructed as shown in FIG. 1, the read signal RF having the writing pulse superposed thereon is equalized by the equalizer 57 shown in FIG. 1, and then the edge pulse is generated by the binarization circuit 59.
Since the read signal RF has a waveform in which it has the writing pulse superposed thereon as above, there is a high possibility that the waveform of the read signal RF after equalized does not have the normal waveform. Also in this respect, it is not possible for the binarization circuit 59 to generate an edge pulse correctly. That is, it is impossible to generate the master clock CLK correctly and detect an address accurately.
It is therefore desirable to overcome the above-mentioned drawbacks of the related art by providing an improved and novel sub data recording apparatus and method and an optical-disk recording medium producing method.